There is so much said here that entire books can be (and have been) written. For the moment it should be enough to consider that these things are all expansions of the core doctrine that John presented in kjv@1John:1 , namely that God is light and in Him is no darkness. If we are in God, so too there can be no darkness in us. Knowing the 'how' this is possible is knowing the 'what' Jesus accomplished in His death and resurrection and the 'who' He is. The working of this knowledge produces unfeigned love in us for the brethren, which is the proof positive of possessing this knowledge. It can be produced in no other way.
Cain is purposely used as the counter example. This key information steers the understanding of this passage a direction it otherwise would not go. The context becomes the inseparable fusion of love and righteousness, it's perceived source/manner and the resultant actions occurring from. Two men make the same effort to worship the living God, the means of which produce two opposite ends. The same can be said of two men that worship, one finding the ability to love unfeigned, the other finding the ability to hate and inflict judgment.
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3